Photovoltaics is a technology that converts radiant light energy (photo) to electricity (voltaics). Photo- voltaic (PV) cells are the basic building blocks of this energy technology. PV cells (also called solar cells) are made of semicon- ductor materials, most typically silicon. The amount of electricity a PV cell produces depends on its size, its conversion efficiency (see box on reverse), and the intensity of the light source. Sunlight is the most common source of the energy used by PV cells to produce an electric current. It takes just a few PV cells to produce enough elec- tricity to power a small watch or solar calculator. For more power, cells are connected together to form larger units called modules. Modules, in turn, are connected to form arrays, and arrays can be interconnected to generate electricity for a large load, such as a group of buildings. Single-crystal silicon is the most common semicon- ductor material used in making PV cells. Polycrys- talline silicon, in the form of a thin film or coating on an inexpensive base of glass or plastic, is also used, and PV modules can also be made of thin films of amorphous (noncrystalline) silicon. Thin films are usually less expensive to manufacture because they require less silicon and the process is less labor-intensive. PV devices are also being devel- oped using combinations of other materials, such as cadmium, copper, indium, gallium, selenium, and tellurium. PV modules are typically installed on or near a building or other structure. They can also be special- ly designed as an integral part of a building’s roof, wall, skylight, or other element. This is called building-integrated PV or BIPV. What are PV energy systems? A PV energy system usually includes a module or array and the structural hardware needed to install it. The simplest PV systems generate DC electricity, usually for a small load, when the sun is shining or they are exposed to artificial light. More complex systems include a power inverter that converts the direct current (DC) generated by PV to alternating current (AC), and batteries that store energy for use at night or when the sun isn’t shining. Today, PV is used primarily for cathodic (corrosion) protection, traffic warning lights, water pumping for irrigation and livestock, telecommunications, security and lighting systems, resource moni- toring, and electric load management. Many of these uses are remote (or off-grid) power gener- ation applications, not connected to utility power lines. PV systems are already used in many off-grid applications in the Federal government, such as for emergency call boxes near interstate highways. When the electricity required for a Federal applica- tion exceeds the amount a PV system can supply, a conventional electric generator can be added to create a hybrid PV/generator system. Wind systems can also be added. PV systems actually have many benefits: • Portability—many kinds of PV systems can be moved about easily. • Reliability—they operate for long periods with little maintenance. • Low operating costs—the fuel is free and there are no (or few) moving parts. • Low environmental impact— they are quiet and nonpolluting (no greenhouse gas emissions). • Stand-alone capability—they operate in remote areas far from power lines. • Modularity—power output can be increased by adding more modules. • Safety—they are not flammable and meet National Electric Code requirements. • Versatility—they operate well in almost any climate. • Short lead time—prepackaged PV systems are available, and utility easements aren’t needed. • Ease of installation—no heavy construction equipment is required. What are some opportunities for using PV in the Federal government? Photovoltaics is a good choice for remote applica- tions in which the daily electric load falls some- where between a few watt-hours and about 100 kilowatt-hours. Because it is nonpolluting, PV Photovoltaics Systems that Convert Sunlight to Electricity Can Meet Many Different Needs FEDERAL ENERGY MANAGEMENT PROGRAM Renewable Energy Technologies for Federal Facilities U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Internet: http://www.eren.doe.gov/femp/ Sandia National Laboratories/PIX01472 PV-powered security lighting at Roosevelt Lake in Arizona.
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Photovoltaics is a technology that converts radiantlight energy (photo) to electricity (voltaics). Photo-voltaic (PV) cells are the basic building blocks of thisenergy technology.
PV cells (also called solar cells) are made of semicon-ductor materials, most typically silicon. The amountof electricity a PV cell produces depends on its size,its conversion efficiency (see box on reverse), andthe intensity of the light source. Sunlight is the mostcommon source of the energy used by PV cells toproduce an electric current.
It takes just a few PV cells to produce enough elec-tricity to power a small watch or solar calculator.For more power, cells are connected together toform larger units called modules. Modules, in turn,are connected to form arrays, and arrays can beinterconnected to generate electricity for a largeload, such as a group of buildings.
Single-crystal silicon is the most common semicon-ductor material used in making PV cells. Polycrys-talline silicon, in the form of a thin film or coating on an inexpensive base of glass or plastic, is alsoused, and PV modules can also be made of thinfilms of amorphous (noncrystalline) silicon. Thinfilms are usually less expensive to manufacturebecause they require less silicon and the process isless labor-intensive. PV devices are also being devel-oped using combinations of other materials, such as cadmium, copper, indium, gallium, selenium, andtellurium.
PV modules are typically installed on or near abuilding or other structure. They can also be special-ly designed as an integral part of a building’s roof,wall, skylight, or other element. This is called building-integrated PV or BIPV.
What are PV energy systems?A PV energy system usually includes a module orarray and the structural hardware needed to installit. The simplest PV systems generate DC electricity,usually for a small load, when the sun is shining orthey are exposed to artificial light. More complexsystems include a power inverter that converts thedirect current (DC) generated by PV to alternatingcurrent (AC), and batteries that store energy for useat night or when the sun isn’t shining.
Today, PV is used primarily for cathodic (corrosion)protection, traffic warning lights, water pumpingfor irrigation and livestock, telecommunications,
security and lighting systems, resource moni-toring, and electric load management. Manyof these uses are remote (or off-grid) power gener-ation applications, not connected to utility powerlines. PV systems are already used in many off-grid applications in the Federal government, such as foremergency call boxes near interstate highways.
When the electricity required for a Federal applica-tion exceeds the amount a PV system can supply, a conventional electric generator can be added tocreate a hybrid PV/generator system. Wind systemscan also be added. PV systems actually have manybenefits:
• Portability—many kinds of PV systems can bemoved about easily.
• Reliability—they operate for longperiods with little maintenance.
• Low operating costs—the fuel is free and there are no (or few)moving parts.
• Low environmental impact—they are quiet and nonpolluting (no greenhouse gas emissions).
• Stand-alone capability—theyoperate in remote areas far frompower lines.
• Modularity—power output can beincreased by adding more modules.
• Safety—they are not flammableand meet National Electric Coderequirements.
• Versatility—they operate well inalmost any climate.
• Short lead time—prepackaged PVsystems are available, and utilityeasements aren’t needed.
• Ease of installation—no heavyconstruction equipment is required.
What are some opportunities for using PV in theFederal government?Photovoltaics is a good choice for remote applica-tions in which the daily electric load falls some-where between a few watt-hours and about100 kilowatt-hours. Because it is nonpolluting, PV
PhotovoltaicsSystems that Convert Sunlight to Electricity Can Meet Many Different Needs
F E D E R A L E N E R G Y M A N A G E M E N T P R O G R A M
RenewableEnergyTechnologiesfor FederalFacilities
U.S. Departmentof Energy
Office of EnergyEfficiency andRenewable Energy
Internet: http://www.eren.doe.gov/femp/
San
dia
Nat
iona
l Lab
orat
orie
s/P
IX01
472
PV-poweredsecurity lightingat RooseveltLake in Arizona.
FEMP Help Desk:800-DOE-EREC
(363-3732)Internet:http://www.eren.doe.gov/femp
Produced for the U.S. Department of Energy by theNational RenewableEnergy Laboratory, a DOE nationallaboratory
DOE/GO-10099-724(a revision ofDOE/GO-10096-272)September 1999
F E D E R A L E N E R G Y M A N A G E M E N T P R O G R A M
Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% post consumer waste
should definitely be considered for remote areas thatrely on fossil-fueled generators for electric power.
On a first-cost basis, the installed cost of a PV sys-tem can be less than the cost of utility service. ButPV may also be a good choice in areas where thereliability of a power plant is questionable, or wherean agency is being charged high rates during peakhours.
The National Park Service has installed more than450 PV systems, chiefly to provide power forresource-monitoring equipment. These are someadditional, widely demonstrated, off-grid applica-tions for PV:
• Lights for walkways, streets, highways, and common areas
• Residential uses (fans, lights, refrigerators) in remote areas
• Electricity for campgrounds, marinas, and offshore drilling platforms
• Equipment for weather stations and fire observation towers
• Communications equipment and facilities (e.g.,emergency roadside phones, microwave repeaterstations)
• Cathodic (corrosion) protection for metal pipesand similar objects
• Highway and warning signs, security systems,transmission tower beacons
• Livestock watering pumps, irrigation systems,and disinfection equipment
• Emergency power during times of crisis.
What is required?Agencies should evaluate different PV systems on the basis of cost, system performance, systemreliability, and maintenance needs. These are someadditional requirements:
• Modules must face south and be unshaded; theycan be mounted on the application (e.g., a highwaysign), on a roof, or on the ground.
• Batteries are often needed to meet peak loads orfor nighttime use; they require periodic maintenance.
• Power inverters will be needed if the load requiresAC electricity.
What does a PV system cost?To determine the economic feasibility of using a PVsystem, agencies should consider these three mainfactors:
• The size and nature of the load
• The availability of the solar resource
• The cost of alternative sources of power.
On a 20-year, life-cycle-cost basis, a remote PV sys-tem typically costs from 25¢–50¢ per kilowatt-hour.In off-grid Federal applications, PV can be morecost-effective than many alternatives. PV equipmentis available from companies listed on the GeneralServices Administration’s Federal Supply Schedule(online, see http://www.gsa.gov/regions/7fss/7fx/schedules). The Federal Energy ManagementProgram has developed specific Energy SavingsPerformance Contracts (ESPCs) that assist Federalagencies in obtaining PV systems (call the FEMPHelp Desk or one of the FEMP contacts below fordetails).
For More InformationFor additional information about PV and ESPCs,contact:
Hal Post (PV)Sandia National Laboratories505-844-2154
John Thornton (PV)National Renewable Energy Laboratory303-384-6469
Nancy Carlisle (FEMP Renewable Energy)National Renewable Energy Laboratory303-384-7509
Tatiana Strainic Muessel (FEMP Project Financing Team Leader)
U.S. Department of Energy202-586-9230
What are the important terms?Balance of system (BOS)—every element (and its associated costs) of a PV system except the modules themselves; this includes the design;land and site preparation; installation; support structures; and powerconditioning, operation and maintenance, and storage equipment.
Break-even cost—the cost of a PV system at which the value of theelectricity it produces equals the cost of electricity from an alternativesource plus the delivery of this electricity to the site; a break-even distance is the distance a power line needs to be extended to matchthe installation cost of a PV system.
Peak watt—the "rated" output of a cell, module, or system; theamount of power a PV device produces when operating at 25°C during tests; the peak rating is usually determined during indoortests rather than outdoors.
PV conversion efficiency—the percentage of available sunlight con-verted to electricity by a PV module or cell; technically, the ratio ofelectric power produced by a cell to the power of the sunlight strikingthe cell.
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